Comparison the kinetic models to estimate the nitrogen mineralization from organic manures in different moisture condition

Extended Abstract
Background and objectives
Knowledge about the rate of nitrogen mineralization from organic matter is very important factor for land management and nitrogen demand of plants. Predicting the availability of nitrogen during the period of plant growth from different fertilizer sources has an important role to increase the fertilizer’s efficiency and to decrease the environmental pollution, too (24). The environmental factors such as temperature and moisture are the most important agents that affect the mineralization processes of nitrogen. Soil moisture regulates the content of oxygen availability and the maximum aerobic activity of micro-organisms is occurred at the range of 50-70% of field capacity soil moisture (9, 15). Most researchers have used the first order model for predicting the nitrogen mineralization potential. Lotfi et al (2008) fund that the first order model had the significant correlation coefficient (P > 0.001) for predicting the mineralization of nitrogen rate and content in a treated soil with cattle manure and sewage sludge. N0K index reflects the potential rate of nitrogen mineralization and is a criterion of nitrogen availability for plants (4). Soodaee Mashaee et al. (2008) investigated the N0K index in livestock manure, vermi-compost, and compost fund that this index was the highest value in livestock manure and the lowest in compost (26). The objective of this research was to study the capability fitting of different models for estimating the content of nitrogen mineralization from different organic sources and to select the best model.
Materials and Methods
In this research, the amount and rate of nitrogen (N) mineralization during 60 days from 4 organic manures (i.e. sewage sludge, poultry manure, cattle manure, and wheat straw) at 2 moisture amounts (40 and 75 % of field capacity) with 3 replications were evaluated. During the experiment, mineralized N was measured with spectrophotometry method and different models were fitted to measured data with least square error method. For selecting the best model, determination coefficient (R2), root mean square error (RMSE), and mean error (ME) were used.
Results
The results showed that although first order, parabolic, logarithmic, and Elovich models had the highest R2 and lowest RMSE, but it was demonstrated that the first order model showed the best fitting to measured data. The highest and lowest values of N availability index (N0k) were observed in poultry manure and wheat straw, respectively. Among the studied treatments, the rate of mineralized nitrogen constant (k) was the lowest value in wheat straw treatment. The mineralized nitrogen (Nmin) and K were increased by increasing the soil moisture content from 40 to 75 % of field capacity.
Conclusion
Due to the first order model was accordant with real condition and appropriate explanation of its parameters, it’s recommended for estimation the N mineralization from organic manures, and the suitable time for application of organic manures in the field can be determined according to the results of this models.